1. Field of the Invention
The present invention relates to a method of manufacturing a spring assembly to be used as, for example, a return spring means for returning a multiple disc clutch piston in a clutch mechanism of an automotive automatic transmission.
2. Description of the Related Art
This kind of related spring assembly (although not concretely shown) includes two annular plates and plural compression coil springs interposed between these annular plates in the circumferential direction thereof at predetermined intervals. At the practical assembling thereof, a state, in which each of the end turn portions of the compression coil springs is set on the outer periphery of a projection portion formed in such a way as to face an associated one of the inner surfaces of the annular plates, is obtained. Then, each of the projection portions is outwardly enlarged in diameter by using a caulking punch. Thus, each of the end turn portions of the compression coil springs is supported by being sandwiched between the outer peripheral surface of an associated one of the projection portions and the inner surface of an associated one of the annular plates.
With such a configuration, in the step of assembling a same-side one of the end turn portions of each of the compression coil springs to an associated one of the annular plates, the caulking punch can easily be made to come closer to an associated one of the projection portions. Thus, the projections can relatively easily be caulked. However, in the step of assembling the other end turn portion of each of the compression coil springs to the associated one of the annular plates, the caulking punch cannot easily be inserted into a region between the annular plates. In this case, extremely difficult and troublesome operations are forcibly performed.
Thus, hitherto, the following method has been proposed as a countermeasure thereagainst. That is, in the case of assembling a same-side one of the end turn portions of each of the compression coil springs to an associated one of the annular plates, the associated one of the projection portions is caulked by using an ordinary caulking punch as heretofore. However, in the case of assembling the other end turn portion of each of the compression coil springs to the associated one of the annular plates, caulking is performed by using a longitudinal split punch and a spreading pin.
Concretely, the longitudinally split punch has an outside diameter that is slightly smaller than the inside diameter of the projection portion. An end portion of the longitudinally split punch is split by a splitting groove in such a manner as to be able to be enlarged. The spreading pin has such an outside diameter that this pin can be inserted into the projection portion associated with the other annular plate. The end portion of the longitudinally split punch can be spread by leading the pointed end portion of the spreading pin into the splitting groove of the longitudinally split punch.
Thus, the end portion of the longitudinally split punch is inserted from the inside of the projection portion associated with one of the annular plate, which has already been caulked, and then made to descend, while the pointed end portion of the spreading pin is faced to the inside of the projection portion provided at the side of the other annular plate to be caulked. Then, the pointed end portion of the spreading pin is led into the splitting groove, so that the end portion of the longitudinally split punch is spread. Consequently, the projection portions can be outwardly spread and caulked (see, for instance, Japanese Patent No. 3288458).
Therefore, according to the related manufacturing method, the projection portion associated with the other annular plate can easily be caulked by using the longitudinally split punch and the spreading pin. Thus, an operation of assembling the other annular plate and the compression coil spring to each other is improved. However, in the case of caulking the projection portion, the projection portion is not uniformly spread over the entire circumference thereof but only partly spread at the end portion thereof, which is split through the splitting groove of the longitudinally split punch. Thus, the holding forces of the compression coil springs against the other annular plate decrease by themselves. Consequently, there is a fear that the compression coil springs may disengage therefrom. Also, the end portion of the longitudinally split punch itself is split through the splitting groove. Thus, the end portion of the longitudinally split punch is poor in strength. Consequently, there is a fear that the longitudinally split punch may easily be broken and abrade away.